1. Field of the Invention
The present invention generally relates to an oxygen concentration detector and a method for producing the same. More particularly, the present invention relates to an oxygen concentration detector that is used for detecting the concentration of oxygen contained in the gas discharged from an internal combustion engine and the method for producing such an oxygen concentration detector.
2. Related Art
Among conventional oxygen concentration detectors used for detecting the concentration of oxygen contained in the exhaust gas from an internal combustion engine, there is one type that includes an element made of a ceramic or zirconia group element, or another group element for generating an electromotive force according to the difference between the concentration of oxygen in a analysis gas and the concentration of oxygen in a reference gas. Electrodes made of platinum or another suitable material are disposed on the face of the above ceramic or zirconia element that is in contact with the analysis gas and on the face of the ceramic or zirconia element that contacts the reference gas, respectively. A detection part comprising alumina particles is disposed on the surface of the electrode at the side that contacts the analysis gas, and a platinum catalyst is supported by the alumina particles.
The above oxygen concentration detector is designed to detect, through a pair of electrodes disposed on the surface of the element formed of an oxygen ion conductive ceramic, the electromotive force generated within the above element according to the concentration of oxygen in the analysis gas.
In the above oxygen concentration detector, the detection characteristics thereof are stabilized by minimizing the influence of variations in the gas components in the exhaust pipe of an engine by using the catalyst provided in the catalyst layer disposed on the analysis gas side of the oxygen concentration detector. In recent years, however, due to increases in the gas mileage achieved by motor vehicles and the improvements in engine performance, the temperature of exhaust gas has also increased and the environments in which such oxygen concentration detectors are utilized have become quite severe. Therefore, the catalyst used in the conventional detector exhibits the problem that it is degraded while in use, thus lowering the responsiveness of the catalyst.